Sound transducer



1969 TADASHI MATSUMOTO 3,480,74C9

SOUND TRANSDUCER 2 Sheets-Sheet 1,

Filed Sept. 16, 1964 Prior arT Inazsn'l'ur TQdQS/QL MaEumoTo w g W %.n

Nov. 25, 1969 TADASHI MATSUMOTO 3,430,740

SOUND TRANSDUCER 2 Sheets-Sheet 3 Filed Sept. 16, 1964 IO A ImzsnTmr Eclashi MaZEumoT'o HTTn United States Patent M 3,480,740 SOUND TRANSDUCER Tadashi Matsumoto, Tokyo, Japan, assignor to Sony Corporation, Shinagawa-ku, Tokyo, Japan, a corporation of Japan Filed Sept. 16, 1964, Ser. No. 396,859 Claims priority, application Japan, Sept. 19, 1963, 38/ 50,179 Int. Cl. H04r 17/02, 19/04 US. Cl. 179---121 Claims ABSTRACT OF THE DISCLOSURE This invention relates generally to an electromechanical transducer and more particularly to a highly sensitive semiconductor device for translating mechanical vibrations into electrical signals. The invention, furthermore, relates to a method of making a semiconductive device which may be employed as an electromechanical transducer.

Semiconductive devices have been utilized in the past as electromechanical transducers for translating mechanical vibrations into electrical variations. However, such prior art transducers possess many disadvantages which are inherent in their structures. These inherent disadvantages result primarily from the present methods of manufacture and design of such semiconductor transducers For instance, presently available electromechanical transducers employing semiconductive materials are of excessively large size and weight as compared to other related devices. A primary consideration, however, is that of output power level of such devices. satisfactorily high output power levels have not been achieved by the prior art semiconductor transducers. Furthermore, constant or stabilized conversion gains and high sensitivities have not been realized.

It is, therefore, one primary object of the present invention to provide an electromechanical transducer having a high output power level.

It is another object of the present invention to provide an electromechanical transducer having a constant and stabilized conversion gain.

Still another object of the instant invention is to provide a semiconductor transducer having high sensitivity.

Still another object of the present invention is to provide an electromechanical transducer which is extremely compact in size and light in Weight.

Yet another object of the instant invention is to provide an electromechanical transducer which employs a planar-type diode or transistor.

These and other objects of the present invention will be more fully realized and understood from the following detailed description when taken in conjunction with the accompanying drawings wherein:

FIGURE l-A is a schematic and diagrammatic view of an electromechanical transducer employing a usual planar type diode;

FIGURE 1-B is a curve illustrating the relationship of current to voltage of the transducer shown in FIGURE l-A;

3,480,740 Patented Nov. 25, 1969 FIGURE 2-A is a schematic and diagrammatic view illustrating an electromechanical transducer employing a usual planar-type transistor;

FIGURE 2-B is a curve illustrating the relationship between collector current and collector voltage of the transducer shown in FIGURE 2-A;

FIGURE 3 is a graph illustrating the novel realizations of the present invention;

FIGURE 4 is a diagrammatic sectional side view of an electromechanical transducer according to the present invention;

FIGURE 5 is a top view of the transducer illustrated in FIGURE 4; and

FIGURE 6 is a sectional view of a microphone in accordance with the present invention.

Like reference numerals throughout the various views of the drawings are intended to designate the same or similar structures.

With particular reference to FIGURE 1A, there is illustrated a planar-type diode of the prior art with an n-type semiconductive layer 2 formed in a p-type semiconductive wafer 1. A stylus 3 is deposited on the surface of the n-type semiconductive layer 2 of the diode for applying point contact pressure thereto. A p-n junction 4 of the diode is defined between the p-type semiconductive wafer 1 and the n-type semiconductive layer 2.

A solid line curve designated with the reference numeral 5 of FIGURE l-B illustrates the voltage versus current characteristic of the diode of FIGURE 1-A. When a pressure P is applied through the stylus 3 to the p-n junction 4 of the diode, the voltage versus current characteristic of the diode varies from the curve 5 to a dotted line curve designated with the reference numeral 6. That is, the current increases with an increase in the pressure P at a particular operating point. Such action is considered to be caused by the p-n junction 4 becoming more ohmic or non-rectifying at that portion where the pressure P is applied. Furthermore, the same eifect can be expected in a planar-type transistor as illustrated by the prior art structure shown in FIGURE 2-A.

The planar-type transistor includes a collector 7, a base 8, and an emitter 9. For purposes of exemplification, the base is illustrated as being an n-type semiconductive layer, the collector 7 is illustrated as a p-type semiconductive wafer and the emitter 9 is illustrated as a p-type semiconductive layer. As illustrated in FIGURE 2-A, the base 8 is formed on the collector 7 and the emitter 9 is formed on the base 8. A p-n junction 4' is defined between the base 8 and the emitter 9 and the stylus 3 is disposed on the emitter for applying a pressure P to the p-n junction. The collector voltage V versus the collector current I characteristic varies as indicated by a curve 5 in FIGURE 2-B. When, however, a pressure P is applied by the stylus 3 to the p-n junction 4' between the emitter and the base of the transistor, the collector voltage versus collector current characteristic is altered as indicated by the dotted line curve designated with the reference numeral 6'. This condition is considered to be caused by the fact that some portion of the p-n junction 4' becomes an ohmic junction and the current amplification degree a of the transistor decreases. Based upon such a phenomenon, the devices illustrated may be employed as electromechanical transducer elements such, for example, as microphones.

In the past, however, fully satisfactory highly sensitive electromechanical transducer elements could not be obtained by the use of such ordinary diodes and transistors. It has been found that the relative distance between the pointed end of the stylus 3 and the p-n junction is of critical importance in determining the particular operating conditions of the device. It has been particularly noted that the nearer the pointed end of the stylus is with respect to the p-n junction, the greater the output voltage or current varies in response to the pressure applied by the stylus to the p-n junction. Thus, a highly sensitive electromechanical transducer can be obtained by making the distance between the stylus 3 and the p-n junction 4' extremely small.

FIGURE 3 illustrates the relationship between changes in collector current AI and the thickness of the emitter 9 designated a. The curve illustrated and the values applied thereto resulted from experiments using a transistor of emitter configuration such as shown in FIGURE 2-A under the conditions that an initial current of 9.6 milliamperes and a constant current of 0.25 milliampere flowed respectively to the collector 7 and base 8 when a weight of 1 gram was applied to the surface of the emitter 9 by the stylus 3. As illustrated in FIGURE 3, the collector current variation AI is less than 0.01 milliamperes when the thickness a of the emitter 9 is more than 2 microns. However, when the thickness a is decreased below 1 micron, for example, to 0.1 micron, the variation AI abruptly increases to approximately 9 milliamperes. Thus, the conversion gain can be appreciably increased by making the thickness a of the emitter 9 as thin as possible, such as, for example, 0.5 micron or less.

In the present practice, an electrode or lead wire is required in the emitter layer and when the thickness at of the emitter is small, the p-n junction between the emitter and base is easily destroyed by thermo-compression bonding for attaching a lead wire or electrode to the emitter. Such conditions cause great difficulty when it is desired to obtain a semiconductive transducer element of high sensitivity.

The present invention is intended to remove such difficulty as experienced in the prior art when it is desired to bond the lead wire or electrode by thermo-compression to the emitter electrode.

The present invention is intended to remove such difficulties experienced in the prior art to provide a highly satisfactory electromechanical transducer. In order to attach the electrode to the emitter, the normal thickness of semiconductive layer is provided at a peripheral or annular portion of the emitter. A central portion of the emitter semiconductive layer within the peripheral portion, however, is made substantially thinner and the stylus 3 is contacted thereto for applying pressures to the device.

The preferred embodiment of the present invention is illustrated in FIGURE 4, wherein the collector 7 is as that shown in FIGURE 2A. In the present preferred exemplification, the structure of the emitter 9 is such that the thickness of a peripheral or annular portion 9a is made relatively large, for example, 1 to microns, sufficient for attaching an electrode 19 or a lead wire thereto and a central portion 9b being contiguous to the peripheral portion 9a is formed as thin ts possible, for example, 0.1 micron. The stylus 3 is contacted with the surface of the central portion 91) for applying pressures thereto in response to mechanical vibrations.

A preferred exemplification of a method for forming such novel configurations is as follows. Firstly, an oxide coating is formed on the surface of the base layer 8 and a thickness of the oxide coating corresponding to the desired thickness of the peripheral portion 9a is removed and a material such as, for example, aluminum, is diffused into the thus exposed limited surface area forming a relatively thick p-type layer. Then, a thickness of the oxide coating corresponding to the desired thickness of the central portion 915 is removed and a shallow p-type layer is formed therein. Thus, the emitter electrode 19 can be attached to the relatively thick peripheral portion 9a, and there is no possibility that the p-n junction will be destroyed by thermo-compression bonding when attaching the electrode or lead wire thereto. According to the present invention exemplified herein, the relatively thin p-type layer 9b for the emitter is of sufiicient area to allow the stylus 3 to be readily contacted therewith. Although the stylus may shift from its initial position due to shock and the like, it is unlikely that it will become disengaged from the central portion 9a due to the relatively large area that can be provided.

The electrode 19 and another electrode 20 are attached to the emitter and base respectively. FIGURE 5 is a top view of the transducer shown in FIGURE 4 and illustrates the emitter electrode 19 and the base electrode 20 as being annular or ring-shaped.

FIGURE. 6 illustrates one preferred embodiment of a microphone employing the novel transducer of the present invention. The housing of the microphone is defined by a base 10, a frame 11 supported on the base 10, and a diaphragm 12 supported on the frame. A pressure transmitting stylus 13 is fixedly mounted at one end thereof to the center of the diaphragm 12. The pointed end of the stylus 13 engages a semiconductive transducer 14 such as that illustrated in FIGURE 4. A header member 15 disposed on the base 10 supports the semiconductive element 14 and an upright support 16 thereon. A rod 21, which may have resilient characteristics, is secured to a mid-point of the stylus 13 and is supported between the upright support 16 and a screw 17. Adjustment of the initial pressure to be applied to the stylus 13 is accomplished by positioning of the screw 17 which is threadedly engaged with the rod 21. It can be appreciated that rotation of the screw 17 in either one of two directions will pre-set the initial pressure applied to the stylus 13 through the rod 21. A plurality of lead pins 18 extend through the base 10 to the electrodes or terminals of the semiconductive element 14.

In the above exemplified microphone, vibrations applied to the diaphragm 12 transmit pressures to the p-n junction of the semiconductive element 14 through the stylus 13. As a result of such pressures, as previously discussed, current flowing through the serniconductive element 14 is accordingly controlled and mechanical vibrations of the diaphragm 12 are translated into electrical variations or vibrations and appear in the lead pins 18.

The teachings of the present invention can similarly be applied to the diode structure illustrated in FIGURE 1-A and a highly sensitive transducer element can be obtained. Furthermore, the present exemplified microphone can similarly employ a diode transducer constructed in accordance with the present invention. It is to be understood that the present invention, although exemplified with particular semiconductive layers, can be applied to n-p-n type semiconductor and, accordingly, substitution of the semi conductive layers with one another is encompassed by the present invention.

The principles of the invention explained in connection with the specific exemplifications thereon will suggest many other applications and modifications of the same. It is accordingly desired that, in constructing the breadth of the appended claims they shall not be limited to the specific details shown and described in connection with the exemplifications thereof.

What is claimed is:

1. An electromechanical transducer comprising a first layer of semiconductor material of a first type and having a central portion and a peripheral portion with the central portion having a thickness of approximately 0.1 micron and the peripheral portion being substantially thicker than said central portion, a second layer of semiconductor material of a second type disposed on said first layer of semiconductor material and conf-ormably shaped to the central and peripheral portions thereof, a stylus in engagement with said central portion of said first layer of semiconductor material, and a pair of electrodes with one of said electrodes attached to the peripheral portion of said first layer of semiconductor material and the other of said electrodes secured to said second layer of semiconductor material.

2. An electromechanical transducer comprising a first layer of semiconductor material of a first type and having a substantially circular central portion Which is relatively thinner than a peripheral portion thereof, a second layer of semiconductor material of a second type disposed on said first layer and conformably shaped thereto, a stylus in engagement with the circular central portion of said first layer, and a pair of electrodes with one of said electrodes attached to the peripheral portion of said first layer and the other of said electrodes secured to said second layer of semiconductor material.

3. An electromechanical transducer comprising a first layer of semiconductor material having a central recessed portion in one surface thereof and said central recessed portion having a thickness of approximately 0.1 micron, a second layer of semiconductor material disposed on said first layer and conformably shaped thereto to enclose all but another surface thereof opposite said one surface, a stylus disposed on the other surface of said first layer opposite said central recessed portion thereof, and a pair of electrodes with one of said electrodes disposed on said second layer of semiconductor material and the other of said electrodes disposed on the other surface adjacent the peripheral edge of said first layer.

4. An electromechanical transducer comprising a housing, a pressure sensitive semiconductor device mounted within said housing and including a first layer of semiconductor material formed with a thin center portion and a thicker outer portion, a second layer of semiconductor material in intimate contact with said first layer of semiconductor material and insulatingly supported by said housing, a pair of leads with one of said leads connected to the thicker outer portion of the first layer and a second lead connected to the second layer, a support connected to said housing, a rod attached to said support, a stylus connected to said rod to support it with one end of said stylus in engagement with the first layer of said semiconductor material at the thin portion thereof, a diaphragm supported by said housing and the other end of said stylus connected to said diaphragm.

5. An electromechanical transducer according to claim 4 comprising means for adjusting said rod relative to the housing to vary the pressure of said stylus on said semiconductor.

References Cited UNITED STATES PATENTS 3,119,947 1/ 1964 Goetzberger 317235 3,241,931 3/1966 Triggs 3l7235 3,403,307 9/ 1968 Rindner 179-110 2,632,062 3/ 1953 Montgomery 179--121 3,295,085 12/ 1966 Nelson 317235 3,312,790 4/ 1967 Sikorski 1791 10 KATHLEEN H. CLAFFY, Primary Examiner A. A. McGILL, Assistant Examiner US. Cl. X.R. 

